Flip chip microelectronic assembly is the direct electrical connection of face-down (hence “flipped”) electronic devices onto substrates by way of conductive bumps on the chip bond pads. The electronic devices are typically semiconductor devices, but may be passive filters, detector arrays, and microelectromechanical system (MEMS) devices. Flip chip is also known as Direct Chip Attach (DCA), since the chip is directly attached to the substrate by the conductive bumps.
The conductive bumps may be attached to the electronic device by ball limiting metallurgy (BLM), also known as under bump metallurgy (UBM) and pad limiting metallurgy (PLM).
Once the electronic device is attached to the substrate, mechanical strains may occur that, over time, result in damage to the conductive bumps and/or to the BLM and/or to a passivation layer of the electronic device.
A non-conductive underfill material introduced to the space between the electronic device and the substrate may protect the bumps from moisture or other environmental hazards, may provide additional mechanical strength to the electronic structure, and may compensate for any thermal expansion differences between the chip and the substrate.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity.